As is well-known in the art, carburetors employ, among other systems, an idle fuel system and a main fuel system. The main fuel system usually comprises a main fuel discharge nozzle (cooperating with related metering restriction means) situated generally within the throat of a venturi section of the induction passage and is therefore responsive to and effective for discharging fuel in accordance with the venturi vacuum generated by the flow of air therethrough. However, generally, at low engine speeds, including idle engine operation, the velocity of air flow through the venturi is insufficient to create a suitable metering vacuum.
Therefore, the idle fuel delivery system, which comprises an idle fuel discharge port communicating with the induction passage, downstream of the throttle valve when in its idle position, is employed to provide the required fuel during the lower range of engine operation. The idle fuel system, by virtue of the location of the idle fuel discharge port, is exposed and responsive to the value or magnitude of the engine intake manifold vacuum generated downstream of the throttle. It should be pointed out that, with certain possible exceptions, the value or magnitude of the manifold vacuum will be the greatest at idle and will diminish as the throttle is progressively moved in an opening direction. Therefore, with merely a fixed idle fuel discharge port, the fuel-air mixture would become leaner in fuel as the throttle were moved in the opening direction because of the fixed discharge area of the idle fuel discharge port and the reduction in the magnitude of the manifold vacuum which reduction accompanies increased throttle valve opening.
Consequently, in order to provide a smooth transition from the idle fuel system (responsive to engine vacuum) to the main fuel system (responsive to venturi vacuum created generally after air flow therethrough has attained a predetermined volocity) the prior art has provided fuel transfer port or slot means communicating with the induction passage and supplied with fuel generally from the idle fuel system. Although the exact location of the lower or terminal portion of such transfer port means is often dependent on the particular characteristics of the engine which is to employ the carburetor, generally, the transfer port means is so located within the induction passage as to be traversed by an edge of the throttle valve as the throttle valve is being moved toward a more fully opened position. In so traversing the transfer port means, the manifold vacuum existing immediately below (downstream of) the throttle valve is permitted to act on the progressively increasing exposed area of the transfer port means thereby increasing fuel flow therethrough and into the induction passage.
Although in years past such transfer port or slot means of the prior art have been generally accepted as being satisfactory, such prior art transfer means or arrangements have now been discovered as being less than satisfactory.
More specifically, the automotive industry has over the years, if for no other reason than seeking competitive advantages, continually exerted substantial efforts to increase the fuel economy of automotive engines. However, the gains continually realized thereby are also continuously being deemed by various governmental bodies as being insufficient with attendant ever-increasing requirements and standards being established regarding both engine fuel economy and engine exhaust emissions. The prior art, in attempting to meet such requirements and standards, has suggested certain improvements to the main fuel metering system of carburetors and to the idle fuel system, more particularly to the idle fuel discharge port and the needle valves employed for determining the effective flow area of such idle fuel discharge port. It has apparently been delivered that such idle fuel discharge ports and main fuel metering systems provided the only areas for improving the fuel economy of a related engine as well as degree of exhaust emissions produced by such associated engine.
It has now been discovered that further significant improvements in both engine fuel economy and levels of engine exhaust emissions are realized by employing a transfer fuel system or arrangement according to the present invention.